STELLAR ORBITAL STUDIES IN NORMAL SPIRAL GALAXIES: EFFECT OF SPIRAL ARMS ON DISK DYNAMICS

We have built a family of non-axisymmetric potential models for normal non-barred spiral galaxies. For this purpose, a three-dimensional self-gravitating model of spiral arms (PERLAS) is used. We analyze the stellar dynamics on the disk plane, varying structural and dynamical parameters such as pitch angle, strength of spiral arms and angular speed. For the pitch angle, we found two limits. The first limit, based on ordered behavior, periodic orbit studies show that for pitch angles up to approximately 15 degrees, 18 degrees, and 20 degrees for Sa, Sb and Sc galaxies, respectively, the spiral arms could be long-lasting structures. Beyond those limits, spiral arms may be explained as transient features rather than long-lasting large-scale structures. In a second limit, from a phase space orbital study based on chaotic behavior, we found that for pitch angles larger than similar to 30 degrees, similar to 40 degrees and similar to 50 degrees for Sa, Sb, and Sc galaxies, respectively, chaotic orbits dominate all the prograde phase space region that surrounds the periodic orbits sculpting the spiral arms, and can even destroy them. Finally, we studied orbital dynamics varying other parameters such as the pattern speed and the spiral arm mass; also we looked for restrictions for these parameters in different morphological types. In these studies we noticed that the effect of spiral arms on the disk dynamics, when we vary the pattern speed and mass, is strongly linked to the pitch angle.